The present invention relates to a direct drawing type lithographic printing plate precursor and, more particularly, to a direct drawing type lithographic printing plate precursor capable of providing a lithographic printing plate which enables to print a great number of printed matter having clear images free from background stain.
Lithographic printing plate precursors which are mainly used at present in the filed of small-scale commercial printing include (1) a direct drawing type lithographic printing plate precursor having a hydrophilic image-receiving layer provided on a water-resistant support, (2) a printing plate precursor having provided on a water-resistant support a lipophilic image-receiving layer comprising zinc oxide, which is converted into a printing plate by undergoing direct drawing image formation and then oil-desensitizing treatment with an oil-desensitizing solution to render the non-image area hydrophilic, (3) a printing plate precursor of an electrophotographic light-sensitive material having provided on a water-resistant support a photoconductive layer comprising photoconductive zinc oxide, which is converted into a printing plate by undergoing image formation and then oil-desensitizing treatment with an oil-desensitizing solution to render the non-image area hydrophilic, and (4) a printing plate precursor of a silver-halide photographic material having a silver halide emulsion layer provided on a water-resistant support.
With the development of office appliances and the expansion of office automation in recent years, it has been desired in the field of printing to adopt an offset printing system wherein a lithographic printing plate is directly prepared from the direct drawing type printing plate precursor (the foregoing (1)) utilizing various image forming means, e.g., an electrophotographic printer, a thermal transfer printer or an ink jet printer without undergoing any other special treatment for conversion into the printing plate.
A conventional direct drawing type lithographic printing plate precursor comprises a support such as paper, having on one surface side thereof an image-receiving layer which is a surface layer provided via an interlayer and on the other surface side thereof a back layer. The interlayer and the back layer are each composed of a water-soluble resin such as PVA or starch, a water-dispersible resin such as a synthetic resin emulsion, and a pigment. The image-receiving layer ordinarily comprises an inorganic pigment, a water-soluble resin and a water resisting agent.
Examples of inorganic pigment used include kaolin, clay, talc, calcium carbonate, silica, titanium oxide, zinc oxide, barium sulfate and alumina.
Examples of water-soluble resin used include polyvinyl alcohol (PVA), modified PVA such as carboxylated PVA, starch and derivatives thereof, cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose, case in, gelatin, polyvinyl pyrrolidone, vinyl acetate-crotonic acid copolymer, and styrene-maleic acid copolymer.
Examples of water resisting agent used include glyoxal, initial condensates of aminoplasts such as melamine-formaldehyde resin and urea-formaldehyde resin, modified polyamide resins such as methylolated polyamide resin, polyamide-polyamine-epichlorohydrin adduct, polyamide epichlorohydrin resin, and modified polyamide-polyimide resin.
It is also known that a cross-linking catalyst such as ammonium chloride or a silane coupling agent can be used in addition to the above described ingredients.
Further, it is proposed that as a binder resin used in an image receiving layer of a direct drawing type lithographic printing plate precursor, a resin having a functional group capable of forming a carboxy group, a hydroxy group, a thiol group, an amino group, a sulfo group or a phosphono group upon decomposition and being previously crosslinked with heat- or light-curing groups included therein is used as described in JP-A-1-226394, JP-A-1-269593 and JP-A-1-288488 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), a resin having the above-described functional group is used together with a heat- or light-curing resin as described in JP-A-1-266546, JP-A-1-275191 and JP-A-1-309068, or a resin having the above-described functional group is used together with a curing agent as described in JP-A-1-267093, JP-A-1-271292 and JP-A-1-309067, for the purpose of improving hydrophilicity of the non-image area, film strength of the image-receiving layer and printing durability.
It is also proposed that into the image-receiving layer, resin particles having a minute particle size of one xcexcm or less and containing a hydrophilic group, for example, a carboxy group, a sulfo group or a phosphono group are incorporated as described in JP-A-4-201387 and JP-A-4-223196, or resin particles having a minute particle size and containing a functional group capable of forming the hydrophilic group as described above upon decomposition are incorporated as described in JP-A-4-319491, JP-A-4-353495, JP-A-5-119545, JP-A-5-58071 and JP-A-5-69684.
However, for improving printing durability of a printing plate obtained by a conventional manner as described above, if the hydrophobicity of the printing plate is enhanced by adding a large amount of the water resisting agent or by using a hydrophobic resin, printing stains due to the decrease in hydrophilicity occur although the printing durability is improved. On the contrary, the enhancement of hydrophilicity results in lowering of the water resistance to cause deterioration of the printing durability.
In particular, when the printing plate is used under a high temperature condition of 30xc2x0 C. or more, it has a defect that the surface layer thereof is dissolved in dampening water used for offset printing to result in deterioration of the printing durability and occurrence of printing stain. Moreover, since images are directly drawn on an image-receiving layer of a printing plate precursor with oil-based ink in the case of direct drawing type lithography, poor adhesion of the oil-based ink to the image receiving layer causes falling off of the oil-based ink in the image area during printing, thereby deteriorating the printing durability even if the occurrence of printing stains in the non-image area is prevented because of sufficient hydrophilicity. This problem does not yet come to a satisfactory solution.
On the other hand, a printing plate precursor having a hydrophilic layer containing titanium oxide, polyvinyl alcohol and hydrolyzed tetramethoxysilane or tetraethoxy-silane as an image-receiving layer has been proposed as described, for example, in JF-A-3-42679 and JP-A-10-268583. As a result of plate-making of such a printing plate precursor to prepare a printing plate and printing using the printing plate, however, it has been practically found that printing durability of the image is insufficient.
The present invention aims to solve these problems which conventional direct drawing type lithographic printing plate precursors have been encountered.
Therefore, an object of the present invention is to provide a direct drawing type lithographic printing plate precursor providing a printing plate free from not only background stain over an entire surface but also dot-like stain.
Another object of the present invention is to provide a direct drawing type lithographic printing plate precursor capable of forming a printing plate which can provide a great number of printed matter having clear images free from background stain and disappearance or distortion of images.
Other objects of the present invention will become apparent from the following description.
It has been found that these objects of the present invention are accomplished with the following direct drawing type lithographic printing plate precursors:
(1) A direct drawing type lithographic printing plate precursor comprising a water-resistant support having provided thereon an image-receiving layer, said image-receiving layer comprising inorganic particles and a binder resin,
wherein the inorganic particles comprise at least one kind of particles selected from:
(i) metal oxide particles having an average particle size of from 0.01 to 5 xcexcm and comprising a metal atom selected from Mg, Ba, Ge, Sn, Zn, Pb, La, Zr, V, Cr, Mo, W, Mn, Co, Ni and Cu; and
(ii) double oxide particles having an average particle size of from 0.01 to 5 xcexcm and comprising at least one metal atom selected from Mg, Al, Si, Ti, Zr, Cr, V, Mo, Sn, W and Nb, and
wherein the binder resin comprises a complex comprising: a resin containing a bond in which a metal atom is connected with an oxygen atom; and an organic polymer containing a group capable of forming a hydrogen bond with the resin and at least one polar functional group selected from a carboxy group, a sulfo group and a phosphono group;
(2) The direct drawing type lithographic printing plate precursor as described in item (1) above, wherein the resin containing a bond in which a metal atom is connected with an oxygen atom is a polymer formed by a hydrolysis polymerization condensation reaction of at least one matallic compound represented by the following formula (I):
(R0)nM0(Y)zxe2x88x92n xe2x80x83xe2x80x83(I) 
wherein R0 represents a hydrogen atoms, a hydrocarbon group or a heterocyclic group; Y represents a reactive group; M0 represents a metal atom having a valence of from 3 to 6; z represents a valence of the metal atom M0; and n represents 0, 1, 2, 3 or 4, provided that the balance of zxe2x88x92n is not less than 2;
(3) The direct drawing type lithographic printing plate precursor as described in item (1) or (2) above, wherein the image-receiving layer has a surface smoothness of not less than 30 seconds/10 ml in terms of a Bekk smoothness; and
(4) A method for the preparation of a lithographic printing plate by an ink jet process comprising ejecting by utilizing an electrostatic field an oil-based ink on a direct drawing type lithographic printing plate precursor to form an image on an image-receiving layer of the lithographic printing plate precursor,
wherein said oil-based ink comprises:
a nonaqueous solvent having an electric resistance of 109 xcexa9.cm or more and a dielectric constant of 3.5 or below; and
charged hydrophobic resin particles, which are solid at least at a normal temperature, dispersed in said nonaqueous solvent, and
wherein said direct drawing type lithographic printing plate precursor is as claimed in item (1) above.